1. Field of the Invention
The present invention relates to a media access controller with a power-save function in a wireless LAN. A media access control layer is part of a data link layer, i.e., the second layer among seven (7) layers of an Open System Interconnection (OSI), and defines a control method of enabling LAN terminals sharing the same transmission line to efficiently use the transmission line.
2. Description of the Related Art
FIG. 1 illustrates basic elements of a wireless local access network (LAN) system provided by IEEE 802.11, which is a standard for a physical layer and a media access control layer in a wireless LAN. A basic unit of the IEEE 802.11 system is basic service sets 101 and 102. In general, the basic service sets are provided with one or more stations 105 and one central base station, referred to as an access point (AP) 103 and 104. The access points (APs) are connected to each other through a distribution system 100, or to other communication networks such as wired or wireless networks.
Additionally, IEEE 802.11 suggests a power management protocol for the media access controller (MAC) so as to reduce power loss of the wireless LAN device. The power management protocol suggested by IEEE 802.11 is classified into two modes, i.e., an active mode and a power-save mode, according to power states of each station 105. The active mode represents that each station operates normally and the power-save mode represents that each station is controlled to reduce unnecessary power consumption when transmission/reception of data through networks are not needed.
During the power-save mode, the stations 105 may sustain data loss since it is impossible for the stations to receive data transmitted to them. Accordingly, stations 105 entering the power-save mode must be changed to the active mode after a predetermined time so as to check data transmitted to them during the power-save mode. Thereafter, data transmitted to each station 105 during the power-save mode is buffered at the access points 103 and 104 of the basic service sets 101 and 102 including each station 105, and then the buffered data are transmitted to each station when each station 105 changes from the power-save mode to the active mode.
As shown in FIG. 2, a time interval in a change from the power-save mode to the active mode is determined by a time interval TDTIM between delivery traffic indication messages (hereinafter, referred to as DTIMs). A basic unit of the TDTIM is a time interval TB referred to as beacon, at which the access points 103 and 104 transmit network information to the basic service sets 101 and 102. As shown in FIG. 2, each station is in a state of the power-save mode during TPS, so that unnecessary power loss is prevented during that time.
FIG. 3 is a basic hardware structure of a general media access controller. Referring to FIG. 3, physical layer interface unit 308 performs an interface function between a physical layer and a media access control layer. Host interface unit 301 performs an interface function between a host and the media access controller. A central processing unit (hereinafter, referred to as CPU) 310 drives the media access controller. Register unit 302 stores information for controlling the media access controller. Local bus 300 connects various peripheral devices 311 with each other. Bus interface unit 304 functions as a bus arbiter and supplies a clock to the media access controller.
Referring to FIG. 4, a general power-save method used in the conventional media access controller disables clocks supplied to each peripheral block 402, 403 and 404 by setting a register 303 which is controllable in software. However, operation of the CPU should be maintained normally at a corresponding time period since the method is carried out in software, so that it is necessary to supply clocks continuously. Thus, unnecessary power loss occurs in the media access controller.